1. Field of the Invention
The present invention relates to a rotating electronic part that is used for composing an input operation unit for various types of electronic devices, for controlling temperature of a car air-conditioner, and for controlling audio and visual signals of a household electronic appliance such as audiovisual equipment; and to a method of manufacturing the rotating electronic part.
2. Background Art
In recent years, there is a demand for a rotating electronic part, which controls volume and images for audiovisual equipment and the like, with a favorable touch and high reliability. A description will be made for such a conventional rotating electronic part, referring to FIG. 7. FIG. 7 is a sectional view of a rotating variable resistor as the conventional rotating electronic part.
Board 1 is a wiring board made of a paper-based phenolic resin laminated sheet or glass epoxy resin laminated sheet. Board 1 is die-cut to provide central hole 1A with a round shape. The top surface has an outer edge formed with resistor element part 1B and an inner side formed with conductive part 1C, concentrically by means of printing or the like. Resistor element part 1B and conductive part 1C are electrically connected to external lead terminals 2 individually swaged to board 1, respectively. Board 1 is fixed to the bottom surface in the recess of case 3 made of insulating resin, by insert molding, so that the surface on which resistor element part 1B and conductive part 1C are provided face to the side of the upper open of the recess.
Wall 3B, a side wall composing a recess in case 3, is formed so as to enclose board 1 to fix the outer edge on board 1. The inner bottom of the recess in case 3 is provided with fit hole 3A with a round shape aligned with central hole 1A on board 1 with the same diameter, in a penetrating state.
Rotor 4 has tubelike shaft 4C and flat-shaped flange 4B. Shaft 4C projecting downward is inserted to central hole 1A and fit hole 3A from up above. The thin-walled bottom end of shaft 4C is swaged in a horn-like shape and combined with case 3 so that rotor 4 is rotatable. Through-hole 4A, provided at the center of shaft 4C, has an oval shape. The top of rotor 4 is provided with flange 4B, which covers the top face of the recess in case 3 with being combined with case 3. Brushes 5, slidingly contacting the tops of resistor element part 1B and conductive part 1C respectively, are fixed to the bottom surface of flange 4B.
The conventional rotating variable resistor structured as mentioned above is used along with a rotation aid or the like fit for oval through-hole 4A of rotor 4, inserted to through-hole 4A. More specifically, when rotor 4 is rotated through a rotation aid or the like, brushes 5, fixed to the bottom surface of flange 4B, slide on resistor element part 1B and conductive part 1C on board 1. Consequently, a resistance value is given between terminals 2 according to the rotating position of brushes 5. Such a rotating variable resistor is disclosed in Japanese Utility Model Unexamined Publication No. H04-97305, for example.
In manufacturing such a rotating variable resistor, board 1 is insert-molded with insulating resin, on the basis of central hole 1A with a round shape on board 1, to form case 3. Therefore, the die-cut shear plane is exposed on the internal end surface of central hole 1A on board 1. As a result, when shaft 4C rotates accompanied by rotation of rotor 4 while contacting the shear plane of central hole 1A, the rough surface of the shear plane causes a rough touch in operation. Meanwhile, if this part is shaved, the powdered shavings may enter conductive part 1C and others on board 1 to be possible to make noise.